Television receivers have recently had a horizontally wide screen and demanded to have a small width and a small thickness as high-definition television and wide-screen television systems are available.
Loudspeakers installed in such a television receiver are often mounted to both sides of the screen, hence increasing the overall width of the television receiver. Such a television receiver generally includes a loudspeaker having an elongated shape, such as a rectangular or elliptical shape. The screen becomes wider, and the loudspeaker are accordingly demanded to have a smaller width. Television receivers have had their image quality increase and accordingly been demanded to have high quality of sound. As thin television receivers including plasma displays or liquid crystal displays have increased, loudspeakers are demanded to have small thickness.
FIG. 13A is a plan view of a conventional loudspeaker 900 disclosed in Patent Document 1. FIG. 13B is a cross sectional view of the loudspeaker 900 at line 13B-13B shown in FIG. 13A. The loudspeaker 900 includes a magnet 901, a plate 902, a yoke 903, a frame 904, a voice coil 905 having a cylindrical shape, and a diaphragm unit 906 having an oval shape. The diaphragm unit 906 has a dome portion 911 having a semicircular cross section provided at the center of the diaphragm unit at the inside of a voice coil 905. The diaphragm unit 906 includes a diaphragm 906B and an edge 912 connected to the outer periphery 906A of the diaphragm 906B. The voice coil drives diaphragm 906B so as to have the diaphragm vibrate to generate sounds. The voice coil 905 is fixed to the diaphragm unit 906. The outer periphery 906A of the diaphragm 906B has an oval shape having straight portions 906C and arcuate portions 906D. The edge 912 has a semicircular cross section. The edge 912 of the diaphragm unit 906 is joined to the frame 904 and supported with the frame 904. More particularly, the diaphragm unit 906 is supported by the frame 904 so that an end of the voice coil 905 is positioned in a magnetic gap provided between the plate 902 and the yoke 903.
Regarding the edge 912 having the semicircular cross section, a change of the curvature of portions of the edge 912 near the arcuate portions 906D of the outer periphery 906A of the diaphragm along a circumferential direction is larger than that of portions of the edge 912 near the straight portions 906C. The portions of the edge 912 near the arcuate portions 906D have stiffness larger than the portions of the edge 912 near the straight portions 906C. The edge 912 is not so elastic along the circumferential direction in response to the vibrating of the diaphragm 906B, and raises the lowest resonance frequency of the loudspeaker 900, accordingly preventing the loudspeaker from reproducing bass sounds. The edge 912 prevents the diaphragm unit 906 from responding to a large amplitude, thus producing distortions.    Patent Document 1: JP 10-191494A